Method of preparing and nitriding a ferrous article



April 9, 1935. A, w. MoRRs 9 9 METHOD OF PREPARINCT AND NITRIDING AFERROUS ARTICLE Filed Dec. 17, 1931 r: I E (C. 14 `I` I A C C I 7 v i ;iI If MG o o G q y l f Z e/ofuj/i I B I 'J /////J////////// Patented Apr.9, 1935 I I 1997,

UNITED SITA'TES PATENT OFFICE METEO!) OF PBEPABING AND NITRmlNG AFERROUS ARTICLE Albert w. Mon-is, Springfleld, Masa., assignor to MooreDrop Forgng Company, Sprlngeld, Masa., a corporation of MassachusettsApplication December 17, 93, seiai No. 581,? 01 4 Claims. (CI. 148-16)This invention relates to a new method of prean electric current throughthe molten bath and paring and nitriding a ferrous article. y theferrous article. Any one or more of these Heretofore, so far as I aminformed, in presubsidiary steps may be used in practicing the paring aferrous article for surface nitrogenizamethod.

5 tion, all the metal in the article has been made The improved methodmay be carried out by 5 of the same mixture or alloy. In other words, tomany forms of apparatus, one of which is shown get a surface suitablefor nitridation, the entire in the accompanying sheet of drawing forminpiece has been made of a nitridable alloy or of the part of thisapplication for patent. same composition throughout its mass. Referringto the drawing:-

o This generally is a disadvantage, first because Fig. 1 is a sectionalelevation, and

of the cost, and second because the elements in- Fig. 2 is a crosssectional view of the apparatus cluded in the article to make itnitridable are shown in Fig. l. usually detrimental to the texture ofthe article Referring more speciflcally to the drawing in and ofteninterfere with or prevent heat treatwhich like reference numeralsindicate like parts, ment. A designates a heating chamber, and B a suit-15 My improved method consists in impregnating able crucible which 'canbe placed in the chamthe surface of the ferrous article to be treatedber A, the crucible having lugs G which positionto a suitable depth witha metal or alloy having the same in the heating chamber. Gas pipesafllnity for'nitrogen. The article thus treated is D-D extend throughthe walls of the chamber 4 then subjected to the action oi* nitrogen sothat a A and a. mixture of air and gas may be led 20 hard nitridedsurface will be obtained on the through these pipes, tangentially intothe annuarticle and whereby the core or 'center of the lar space betweenthe heating chamber and article will be practically untreated and willrecrucible so that the metal in the crucibie can be tain thecharacteristics due to its original comkept in molten condition and at asuitable temposition or alloy. perature. 25

By my method almst any ferrous alloy hav- E designates a cover platewhich is adapted ing good properties of strength and that will be torest upon the top rim of the crucible B. This insensible to temperingbrittleness can be used, cover plate may be tightly clamped to the'topthus ensuring better castings, forgings and perof the crucible by screwsF', which are pivoted ao mitting heat treatment of ferrous articles hav-,in the lugs G on crucble and which screws ing nitrided surfaces. fitbetween ears (U ormed. on the rim of the My method may be carried out asfollows:- cover plate E, huta H being threaded on the After making theferrous article in the form screws F. desired, either by casting orforging I immerse A packing or bear-ing washer may be placed on or dipit, while hot and preferably heated to a top of the c'ucible. The coverplate E may be 35 temperature above 12007 Fahrenheit, in a bath providedwith a. stumng box I through which a oi' molten metal having aflinityfor nitrogen. plunger J can be reciprocated for purposes here- This bathis preferably molten aluminum either matter described. This plunger maybe made pure or alloyed with zirconium, titanium, of graphite or mayhave its surface coated with 40 chromium, vanadium, magnesium,beryllium, graphite. Extending from the cover plate is a 40 silicon,nickel, molybdenum, manganese, or any notched flange K for holding theferrous articles desred combination of these, known in the art to betreated.. for alloying with iron to make up a nitridable Practically anyieri-aus article can be treated in the apparatus above described. Asshown a I have found by thus treating a ferrous article umbe of autmobil rank shafts L are being 4: that there will be a surfaceimpregnation thereof treated. with the above described apparatus, to aco ab d p by e metal or alloy the crank shafts L after being shapedeither by havin aflinity for nitrogen. forging or casting are placed inthe notches in I have also found that I can increase both the flange K,

60 the depth and amount of the impregnation of Care should be taken tokeep the articles from ferrous article either by subjecting the bath oftouching each other, while in the bath, as such molten metal havingaflinity for nitrogen to touching would hinder impregnation of theartihydrostatic pressure, by agitating the bath durcles at the `pointsof contact and would result ing impregnation, by removing the air andusing in thin spots in the coating.

nitrogen on the surface of the bath, or by passing These crank shafts orferrous articles to be 55 treated when placed in position should bevery` hot, preferably heated to a temperature above 1200 Fahrenheit.This temperature can be obtained by taking the articles while they arehot from forging or casting or they can be heated to the desiredtemperature before being placed in the notches.

The crucible is filled with a bath of molten metal or alloy havingafllnity for nitrogen. The metal 'or alloy thus employed is preferablyalumi- .num or any alloy that is known in the art as useful foreffecting nitrogenization.

This bath is kept at the proper temperature by the gas jets D-Dpreviously described.

The cover plate is then placed in position on the crucible and tightlyclamped thereto so that the hot ferrous articles will be immersed ordipped in the bath of molten metal. The articles are kept, in the bath asuitable length of time.

During the treatment in the bath, care should be used'to see that thesurface of the ferrous articles to be impregnated is clean and free fromscale.

I 'found that under these conditions, the metal or alloy having afllnityfor nitrogen will penetrate to a suflicient depth into the surface ofthe ferrous articles being treated to permit them to be nitrided afterbeing machined to size.

This impregnation is accelerated by depressing the plunger J to create ahydrostatic pressure between the bath and the articles, or byreciprocating the plunger to agitate the bath during impregnation.

After this treatment the cover plate is removed and the ferrous articlesare allowed to cool. They then may be subjected to-a flnishing processthe only surfaces which will be hardened or nitrided will be thebearings and the crank pins or journals;

The nitrogen will unite with the metal having an afiinity for nitrogenwhich has impregnated 'into the surface of the ferrous article.

Thus a ferrous article will be produced having any desired ferrous.composition in its core and having a 'hard nitrided surface orsurfaces. This article will thus have' the. advantages previously manyother forms of apparatus may be devised V whereby the surfaceimpregnation, which is the principal feature of my invention, can bepracticed. i

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent of the United States is:-

1. The method of nitriding a ferrous article which consists in heatingthe article to a temperature of at least 1200 F. and immersing thearticle while heated in a bath of molten metal having amnity fornitrogen and composed at least in part of aluminum, and agitating themolten metal by applying and removing a hydrostatic pressure on thebath, to obtain a surface impregnation of the ferrous article with saidmetal, removing the article from the bath and thereafter hardening thesurface thereof by nitridation. i

2. The method of treating a ferrous article which consists in heatingthe article to a temperature of at least 1200" F. and in immer'sing thearticle while heated in a bath of molten metal having afllnity fornitrogen and composed at least in part of aluminum, placing the bathunder a hydrostatic pressure to obtain a surface impregnation of theferrous article with said metal, removing the article from the bath andthereafter hardening the surface thereof by nitrldation.

3. The method of. treating a ferrous article, which consists in heatingthe article to a temperature of at least 1200 F. and in immersing thearticle while heated in a bath of molten metal having afllnity fornitrogen and composed at least in part of aluminum, agitating the moltenmetal to obtain a surface impregnation of the ferrous article with saidmetal, removing the article from the bath and thereafter hardening thesurface thereof by nitridation.

4. The method of nitriding a ferrous article, which consists in heatingthe article to a temperature over 1200 E., and immersing the articlewhile eo heated in a bath of molten metal having amnity for nitrogen andcomposed at least'in part of aluminum, to obtain a surface impregnationof the ferrous article with said metal and thereafter removing thearticle from ,the bath and subiecting the-impresnated article tohardenlns by nitrldation.

ALBERT W. NORRIS.

